This invention relates to electromagnetic heating and in particular to a fastener to be used between two thermoplastic objects for induction heating and joining purposes.
Induction heating using a metal fastener is known in the art. The metal fastener may be a solid sheet of eddy-current conducting metal placed adjacent to the materials to be joined, or an apertured or screened sheet placed between the materials. Electromagnetic induction heats the metal when one of several known induction heating methods is used; the heat generated softens and joins the nonmetallic material.
Often the step following the joining of thermoplastics is that of providing electronic circuitry thereupon. An electrical conduction system is usually separately fabricated and fastened to the joined materials. No means have been provided for inductively heating sheets and simultaneously fixing electronic circuitry into the system.
Metallic conductive particles have been introduced into the adhesive which bonds circuit subassemblies, as in U.S. Pat. No. 3,795,047. These metallic particles join the conductive elements of the joined subassemblies. This method has been found useful when objects are joined by lamination technique, and when the distance between the conductive elements is small. The technique described is of little help in induction heating, however, where metal particles would short circuit upon their almost certain contact with inductor wires, and where the heat generated is high. Also, in, for example, a large space structure, electricity may travel miles along a circuit, and metal particles are not efficient or reliable enough to cover such a distance.
Heating wires have been incorporated between laminated panels, as in U.S. Pat. No. 3,629,040. These heating wires carry no insulation, and, as mentioned before, would short circuit upon contact with induction heating wires.
There has been no means provided in the art for including electrically conductive elements within sheets of material to be joined by induction heat, nor has there been provided a technique for joining thermoplastics and including conductive wires in a system in one step. An object of the present inventin is, therefore, to provide such a method and apparatus.
Another object of the invention is to provide such a method and apparatus, which may be used in motionless environments or in the vacuum of outer space.
Yet another object of the present invention is to provide a fastener for use in inductive heating and joining or organic composites, wherein the inductive and conductive elements are wires.
Still another object of the present invention is to provide such a fastener, wherein the inductive and conductive elements are integrated in a screened arrangement.